1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device having a digitizer and a method for fabricating the same. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for providing a fixing device for fixing the digitizer to a liquid crystal display module for improving an operation efficiency and providing a stable composition in the process of assembling the liquid crystal display module and the digitizer.
2. Discussion of the Related Art
Resolution of liquid crystal display (hereinafter referred to as “LCD”) devices has been rapidly developed by the improvement of liquid crystal materials and micro fabrication technology with their characteristics of lightweight, thin profile, and low power consumption. Also, the liquid crystal display device has been widely used in various applications. For example, the LCD device is used as a display device of a notebook personal computer (hereinafter referred to as “NTPC”). The NTPC is slim and lightweight, so that the user can use information on the move. Among video display devices applied to various display devices, particularly, the liquid crystal display module (hereinafter referred to as “LCM”) including a backlight unit and a liquid crystal display panel, which is a flat-panel display, will now be explained.
FIG. 1 is an expanded view of the related art liquid crystal display device. As shown in FIG. 1, the liquid crystal display module 10 includes a backlight unit 12 and a liquid crystal display panel 11.
The backlight unit 12 includes a light source (not shown) radiating light, a reflecting plate 12a reflecting light from the light source in one direction, a light guiding plate 12b guiding light from the light source to the entire surface of the liquid crystal display panel, a first diffusing or protective sheet 12c, a first prism sheet 12d, a second prism sheet 12e, and a second diffusing or protective sheet 12f. Each of the polarizing plates 11a and 11b is provided at both sides of the liquid crystal display panel 11.
The backlight unit 12 and the liquid crystal display panel 11 are supported by a support main 13 and a top case 20. More specifically, the reflecting plate 12a, the light guiding plate 12b, the first diffusing or protective sheet 12c, the first prism sheet 12d, the second prism sheet 12e, and the second diffusing or protective sheet 12f are stacked on the upper surface of the support main 13 of a plastic material. The liquid crystal display panel 11 having the polarizing plates 11a and 11b on each surface thereof is stacked on the diffusing or protective sheet 12f. The liquid crystal display panel is coupled with the top case 20 formed of steel at the top and is supported by the support main 13 at the bottom.
Recently, high resolution of a liquid crystal display device is realized with the improvement of LCD technology, and thus, a high-resolution graphic work can be realized. Therefore, a touch panel is also used as an input device in the NTPC.
Also, the touch panel provided in the NTPC can be applied to a device performing the same function as a touch screen of a cathode ray tube (CRT) used in a desktop computer.
The touch panel provided in the NTPC can be classified into a resistive film type, an electrostatic capacitance type, and an electromagnetic (EM) type depending upon the method of searching a user-directed position.
The touch panel of the resistive film type detects a position of a touching point by the change of an output current when a direct current voltage is applied to the touch panel. The touch panel of the electrostatic capacitance type detects the position of the touching point by using capacitance coupling when an alternating current voltage is applied to the touch panel. The electromagnetic type detects the position of a touching point by detecting a resonance frequency when a magnetic field is applied to the touch panel.
Since each type has different characteristics of a signal amplification problem, a resolution difference and a different degree of difficulty in design and technology, a specific type should be chosen for merit. Optical, electrical, mechanical, weather resistant and input characteristics as well as endurance and economical efficiency should be considered in choosing a specific type.
The development of the EM type touch panel draws attention due to its distinction of the accurate position among the touch panels. The EM touch panel includes a digitizer having two sets of array coils, one set of which is parallel to the other set, and an electronic pan handing in a position on the digitizer.
Hereinafter, the related art electromagnetic touch panel will be explained with reference to the accompanying drawings. FIG. 2 illustrates a schematic view of the related art liquid crystal display device having the electromagnetic touch panel.
As shown in FIG. 2, the related art liquid crystal display device having an electromagnetic touch panel includes a liquid crystal display panel 11 having upper and lower substrates, a liquid crystal layer between the upper and lower substrates to display a video signal according to scan signals and data, a backlight unit 12 radiating light and uniformly irradiating the light at a rear portion of the liquid crystal display panel, a sensor unit 29 sensing a touched position by receiving a resonance frequency in accordance with the position where an electronic pen 39 is touched, a control unit 15 controlling the sensor unit 29, a top case (shown in FIG. 1) supporting the liquid crystal display panel 11, the backlight unit 12, the sensor unit 29, and the control unit 15 with a single body, and an electronic pen 39 communicating with the sensor unit 29 by transmitting and receiving the resonance frequency.
The sensor unit 29 and the control unit 15 are referred to as an electromagnetic touch panel or a digitizer. Although it is not shown, a passivation layer spaced apart from the liquid crystal display panel 11 and protecting the liquid crystal display panel 11 is further included at a top portion of the liquid crystal display panel 11.
The sensor unit 29 includes a sensor printed circuit board (PCB) having a plurality of X-axis coils and Y-axis coils, a shield plate blocking electromagnetic wave at a bottom portion of the sensor PCB and a connector having a switching device for directing transmission and receiving modes of the sensor PCB and choosing the X or Y axis coils.
The control unit 15 located at the bottom portion of the sensor unit 29 includes a control processor unit sending a signal to the sensor unit 29 and reading the input signal so as to detect the position of the electronic pen 39. The electronic pen 39 includes a resonance circuit having a coil and a condenser therein.
The structure of the digitizer including the sensor unit and the control unit will be explained as follows. FIG. 3 is a block configuration diagram illustrating a driving circuit of an electromagnetic digitizer. As shown in FIG. 3, the sensor unit 29 of the digitizer 40 includes X-axis and Y-axis coil arrays and X-MUX and Y-MUX coupled to the X-axis and Y-axis, respectively. A specific Y-axis coil is chosen by a Y address signal (Y-ADDR), and a specific X-axis coil is chosen by an X address signal (X-ADDR) for reading. Herein, both X and Y address signals are generated from the control unit 15.
A sine wave and an electron wave are sent to the X-axis and the Y-axis by the control unit 15, and the output signals from the X-axis and Y-axis coil are sent to the control unit 15. The control unit 15 includes a sine wave generator 31 generating and sending the sine wave to the coils, an amplifier 32 amplifying the sine wave generated from the sine wave generator 31, a switch 30 sending the amplified sine wave to the coil or sending a signal from the coil to the control unit 15, an amplifier 34 differentially amplifying an output signal generated from the coil by the switch 30, a wave detector 35 (WD) detecting waves from the amplifier 34, a low pass filter 36 filtering the output signal generated from the wave detector 35, a sample and hold unit 37 (S/H) sampling, holding, and outputting a signal generated from the low pass filter 36, an analog-digital converter 38 converting size and polarity of an analog signal outputted from the sample and hold unit 37 to a digital format and outputting the digital signal, and a processor 33 reading the output signals from the analog-digital converter 38 for locating the position of the electronic pen 39 and controlling every unit. While the analog-digital converter 38 is digitizing a measured value of a coil, the sample and hold unit 37 holds the value, and a subsequent second coil begins to measure a sine wave in the previous circuits.
The digitizer 40 includes a plurality of coils overlapping the flexible surface of the PCB. Each coil is arrayed with respect to the X-axis and the Y-axis, and has one side connected to the ground voltage and the other side connected to a MUX unit to apply to an electric potential line of a fixed level.
The operation of the electromagnetic touch panel is as follows. The sine wave generated from the sine wave generator 31 by a control signal of the processor 33 is transmitted to the sensor unit 29 through the amplifier 32 and the switch 30. The sensor unit 29 chooses an X-axis coil and a Y-axis coil to generate an electromagnetic wave by inducing an electromagnetic wave. The electronic pen 39 is resonated, the resonant frequency is held for a predetermined period of time, and the sensor unit 29 receives the electromagnetic wave generated from the electronic pen 39.
The electronic pen 39 includes the resonance circuit. The resonance circuit is an RLC resonant circuit in which the maximum electric current flows at a specific frequency of an applied voltage. The resonant frequency can be expressed to show output characteristics at a specific resonant frequency. In other words, the resonant frequency (f) is expressed as a mathematic formula as
      f    =          1              2        ⁢        π        ⁢                  LC                      ,wherein, L represents an inductance of a coil and C is a capacity of the condenser.
Depending upon the position of the electronic pen 39, each sine wave voltage having a different value is induced to each coil arrayed in the sensor unit 29 and inputted into the processor 33 through the wave detector 35 and the analog-digital converter 38.
The processor 33 calculates the value of the position of the electronic pen 39 on the digitizer 40 from the value induced to the coil and outputs an angle value between 0 and 360 degrees. The output data of the electronic pen 39 are stored in the processor 33.
It is convenient for a user to draw a figure when an area of the electromagnetic digitizer is larger and more efficient when the resolution is higher. The resolution is inversely proportional to the gaps between each coil in the digitizer 40. That is, when the gaps between the coils are narrower, the resolution becomes higher.
The electromagnetic touch panel using a completely different method from the resistant film type detects the exact position of the electronic pen by using the characteristic of an electromagnetic field being induced and resonated. The electromagnetic touch panel uses a stable method, which does not influence the image quality, and includes the sensor unit and the control unit at the rear portion of a display device so as to have a high transmittance of the display device. The electromagnetic touch panel is not influenced by a mere hand touch but only by the touch of a pen, and the writing is as natural as handwriting. Therefore, it is used in design works, academic presentations, and seminars.
Meanwhile, FIG. 4 is a rear view of the digitizer provided in the liquid crystal display module. In general, a printed circuit board 45 (hereinafter referred to as “PCB”) is provided at the rear surface of the support main 13 at the bottom of the liquid crystal display module 10. A drive integrated circuit (hereinafter referred to as “D-IC”) for driving a gate line and a data line of the liquid crystal display panel is provided at the PCB 45. And, the liquid crystal display module 10 and the PCB 45 having the D-IC are electrically connected by a tape carrier package 14 (hereinafter referred to as “TCP”), so as to send a control signal of the D-ICs (a gate line driving signal) and a video signal (a data line driving signal) to each gate line and data line of the liquid crystal display panel. Although there are some differences depending upon the products, a PCB 45a having a drive IC for driving the data line is connected to the TCP 14 at a corner in the long axis direction of the liquid crystal display panel and the PCB 45b having the drive IC for driving the gate line at a corner in the shorter axis direction of the liquid crystal display panel.
Accordingly, the LCM is driven by a control signal and a video signal of the D-IC provided at the PCB 45 and changes the structure of the alignment of liquid crystals. A picture corresponding to the video signal is displayed by a light channel formed according to the alignment of liquid crystals on the liquid crystal display device.
Therefore, when the digitizer is formed at the rear portion of the LCM, it is desirable that the electro-magnetically uniform LCM is arrayed on the top portion of the digitizer and an electro-magnetically uneven material in an irregular form, such as PCB, is provided on the bottom portion of the digitizer.
An assembling method for a liquid crystal display device having an EM type touch panel, as shown in FIG. 4, is to insert the digitizer between the support main 13 and the PCB 45 after the LCM 10 is assembled, the PCB 45 having a drive IC for driving the liquid crystal display panel. When inserting the digitizer, as shown in FIG. 4, the PCB 45 should be lifted upward and the digitizer is fixed to the PCB 45 at the predetermined position to reduce damage in the TCP 14 electrically connecting the PCB 45 to the liquid crystal display module 10 (shown in FIG. 4 as arrows)
However, there are problems in lifting the PCB 45 and fixing the digitizer, which will be described as follows. First, when the digitizer 40 is fixed, the inserted digitizer, the PCB 45, and the TCP 14 are contacted and damaged, thereby increasing product deficiency. Also, when the PCB 45 and the TCP 14 are lifted to insert the digitizer, the TCP 14 connected to the PCB 45 is contacted with the top case 20 and cracked. Particularly, product deficiency is increased when the PCB 45 is provided at both corners of the long and short axis directions of the liquid crystal display panel. Furthermore, when an end portion of the top case 20 has a burr having a sharp end because an end due to the deficient end portion of the top case contacting the TCP, the damage of the TCP is accelerated.
Second, the PCB is fastened with a screw leaving a necessary space between the support main and the PCB so as to insert the digitizer into the space according to the related art. The LCD becomes larger in size to provide an extra space for fixing the LCM with a screw, thereby producing a lightweight and slim size LCD without having a digitizer provided thereto.
Therefore, when the digitizer is inserted between the LCM and PCB, there is a problem in that the PCB should be lifted and the PCB and the TCP are damaged, thereby increasing product deficiency.